Method for utilizing a fixed catalyst bed in separate hydrogenation processes

ABSTRACT

Middle distillate virgin oils, such as straight run furnace oil, jet fuel or kerosene are required to meet many commercial specifications, among which are maximum allowable total sulfur content, maximum allowable mercaptan sulfur content and maximum allowable total acid number. Middle distillates which do not meet commercial specifications in regard to total sulfur content can be hydrodesulfurized for the removal of the portion of the total sulfur required for meeting the commercial requirement. Such hydrodesulfurization requires more severe conditions than do processes for reduction of total acid number or for reduction of mercaptan sulfur content so that under the severe conditions required for hydrodesulfurization, excessive total acid number and excessive mercaptan content are automatically concomitantly reduced to commercially acceptable levels. The present invention relates to the hydrotreatment of virgin middle distillates which meet commercial specifications in regard to total sulfur content in the absence of prior hydrotreating or any other treatment, but do not meet commercial specifications in regard to total acid number or in regard to mercaptan sulfur content. According to the present invention, the latter middle distillates are not blended with high total sulfur feeds flowing to hydrodesulfurization processes requiring severe conditions to accomplish reduction in total sulfur content, but are hydrotreated separately under relatively more mild catalytic hydrotreating conditions to reduce mercaptan sulfur content or total acid number at hydrotreating severities which are so mild that there is an extremely limited consumption of hydrogen and a very limited removal of total sulfur. The catalyst employed in the mild hydrotreating processes of this invention is a deactivated hydrotreating catalyst from a more severe hydrodesulfurization or other hydrotreating operation which is no longer of viable use in the more severe operation due to numerous cycles of use and regeneration, due to excessive metals deposit thereon, or any other reason.

United States Patent 1191 Plundo et a1.

[ Nov. 26, 1974 METHOD FOR UTILIZING A FIXED CATALYST BED IN SEPARATEHYDROGENATION PROCESSES [75] Inventors: Robert A. PIundo, Greensbur g;

Thomas C. Readal, McCandless Township; James R. Strom, OHara Township,all of Pa.

[73] Assignee: (gulf Research & Development Company, Pittsburgh, Pa.

22 Filed: Feb. 27, 1973 21 Appl. No.: 336,384

[52] US. Cl 208/210, 208/15, 208/216, 208/263, 208/264 [51] Int. Cl.Clog 31/14 [58] Field of Search 208/210, 216, 263, 264, 208/15 [56]References Cited UNITED STATES PATENTS 2.401.334 6/1946 Burk et a1.208/216 2,717,857 9/1955 Bronson et a1. 208/216 2,793,986 5/1957 Lanning208/264 2,921,023 l/l960 Holm 208/263 2.963.425 12/1960 Hansen 208/2162,998,381 8/1961 Bushnell 208/216 3.413.216 11/1968 Doumani 20812163,483.1 19 12/1969 Ehrler 208/264 Primary Examiner-Delbert E. GantzAssistant Examiner-C. E. Spresser [57] ABSTRACT Middle distillate virginoils, such as straight run furnace oil, jet fuel or kerosene arerequired to meet many commercial specifications, among which are maximumallowable total sulfur content, maximum allowable mercaptan sulfurcontent and maximum allowable total acid number. Middle distillateswhich do not meet commercial specifications in regard to total sulfurcontent can be hydrodesulfurized for the removal of the portion of thetotal sulfur required for meeting the commercial requirement. Suchhydrodesulfurization requires more severe conditions than do processesfor reduction of total acid number or for reduction of mercaptan sulfurcontent so that under the severe conditions required forhydrodesulfurization, excessive total acid number and excessivemercaptan content are automatically concomitantly reduced tocommercially acceptable levels. The present invention relates to thehydrotreatment of virgin middle distillates which meet commercialspecifications in regard to total sulfur content in the absence of priorhydrotreating or any other treatment, but do not meet commercialspecifications in regard to total acid number or in regard to mercaptansulfur content. According to the present invention, the latter middledistillates are not blended with high total sulfur feeds flowing tohydrodesulfurization processes requiring severe conditions to accomplishreduction in total sulfur content, but are hydrotreated separately underrelatively more mild catalytic hydrotreating conditions to reducemercaptan sulfur content or total acid number at hydrotreatingseverities which are so mild that there is an extremely limitedconsumption of hydrogen and a very limited removal of total sulfur. Thecatalyst employed in the mild hydrotreating processes of this inventionis a deactivated hydrotreating catalyst from a more severehydrodesulfurization or other hydrotreating operation which is no longerof viable use in the more severe operation due to numerous cycles of useand regeneration, due to excessive metals deposit thereon, or any otherreason.

27 Claims, 8 Drawing Figures 2 o: W 3 Q u. n: .014 I 0.. (I) j. I .012 51- L" l 3 .010 T 3 a: Z T 11 .1 10 5 .008

E g 5 as .006 z 5 g 9 D 5 (I) .004 L 3 Z 0 1 LLI O: 9; .002 7 P 3: 2 LuL11 1 2 0.000 v 400 450 500 5 (204C) (232%.) (260C) 0.

REACTDR TEMPERATURE F PAIENTEDmvzswm sum 1 or 4 FIG.

NON- MERCAPTAN DESULFURIZATION WEIGHT PERCENT EROS ENE X SOUTH LOUISIANAK SOUTH LOU SIANA FURNACE JIL 60 8O NON-MERCAPTAN DESULFURIZATIC JN,

WEIGHT PERCENT PATENTED REV 28 {974 SHEET 2 UP 4 FIG. 3

O OOOOO OOOOO 0 6 432 2528 25 $523. wziomm 2. 2253mm E355 NON- MERCAPTANDESULFURIZATION,

WEiGHT PERCENT FIG. -4

3.0 0 5 0 5 O 7 m 8 8 9 9 n v YZLI:

REACTOR TEMPERATURE F mmmm Q PATENTED HUV 2 8 I974 TOTAL ACID NUMBER,D664 TOTAL DESULFURIZATICON,

WEIGHT PERCENT SHEET U 0F 4 REACTOR TEMPERATURE: F

FIG. 6

FRESH cATALYsTEE/ I I I 60 CATALYST AT FIFT-i CYCTJI 50 I (3lO'C.)(326'C.) (338'CJ (349C) (360'0) (37lC.) (382(2) AVERAGE REACTORTEMPERATURE: F.

N PERCENT REDUCTTON TN TOTAL ACID NO. 0664 METHOD FOR UTILIZING A FIXEDCATALYST BED IN SEPARATE I-IYDROGENATION PROCESSES This inventionrelates to a very mild hydrotreatment of virgin middle distillates suchas furnace oil, kerosene, jet fuels, light gas oils or diesel oils inorder to reduce the total acid number or the mercaptan content of thedistillate without greatly reducing the total sulfur content of the oilsin the presence of a catalyst which has previously been deactivated in amore severe hydrotreating process. This invention is related to twopatent applications filed by the same inventors on even date herewithentitled Method for Reducing the Total Acid Number of a MiddleDistillate Oil" and Method for Reducing the Mercaptan Content of aMiddle Distillate Oil bearing Ser. Nos. 336,382 and 336,383,respectively.

The middle distillates of this invention boil generally above thenaphtha range and generally exclude lubricating oils.

Middle distillates which do not meet commercial requirements in regardto total sulfur content, which is about 0.2 weight percent sulfur forfuel oils destined for use as home heating fuel, are commonlyhydrodesulfurized under relatively severe conditions in order to reducethe total sulfur content to a level of at least as low as the commercialrequirement. Such hydrodesulfurization processes generally occur in thepresence of a Group V] and Group VIII metal containing catalyst such ascobalt-molybdenum nickel-cobaltmolybdenum or Nickel-tungsten on anon-cracking support such as alumina or alumina with a small stabilizingbut non-cracking amount of silica which can be, for example, less than0.5 percent, or less than than 1 percent by weight. Common severehydrodesulfurization conditions include a temperature range between 650or 675 and 800F. (343 or 357 and 427C), a pressure of at least 600 psig(42 kglcm and more generally in the range between 1,000 and 2,000 or3,000 psig (70 and 140 or 210 kg/cm a liquid hourly space velocitybetween about 0.7 and 2 and a hydrogen circulation rate of between about2,000 and 3,000 standard cubic feet per barrel of hydrogen (36 and 54SCM/lOOL), which hydrogen can be about 75 to 80 percent pure. Hydrogenconsumption is commonly about 400 standard cubic feet per barrel (72SCM/lL) at 1,000 psi (70 kg/cm") operation or about 500 standard cubicfeet per barrel (9 SCM/IOOL) at 2,000 psi (I40 kglcm operation. Theseare only examples of severe hydrodesulfurization conditions, and arenon-limiting.

ln refinery operations utilizing such hydrodesulfurization operations,virgin middle distillates from a multiplicity of crude oil sources arecommonly combined for feeding to such high pressure hydrodesulfurizers.The various middle distillates that are combined may individually failto meet commercial specifications in regard to less than all standards.A middle distillate which falls to meet commercial requirements inregard to total sulfur content must be treated under the severe highpressure desulfurization conditions described above. However, inaccordance with the present invention it has been found that a straightrun middle distillate which does meetcommercial total sulfurrequirements in the absence of any prior hydrotreatment but fails tomeet commercial total acid number requirements and/or commercialmercaptan requirements need not be blended with the high total sulfurfuel can be treated separately in a different reactor under more mildconditions without employing a fresh catalyst but rather employing acatalyst that has been deactivated in a separate reactor underrelatively more severe hydrogenation or hydrodesulfurizattion conditionsto a state that its use is no longer visible in the severe hydrogenationoperation.

High total acid numbers in oils are primarily due to the presence ofnaphthenic acids in the oil. The acid attacks copper and zinc in fuelhandling systems. This type of metals pick-up not only induces metallosses in pipelines which affect metal ratios in alloys but also causesinstability leading to sludge formation in the oil which can cause theoil to deposit sludge on injectors, float controls and other criticalparts. In one known case a hign neutralization number diesel oil wasfound to pick up sufficient zinc from a diesel engine to cause engineshutdown. Harmful effects in equipment due to high copper pick-up withemploying a high total acid number oil have also been experienced. Forthese reasons, commerical specifications in the United States requiretotal acid numbers in oils to be below oil as determined by either oftwo ASTM test methods disclosed below while European commercialspecifications generally require total acid numbers below 0.2.

Mercaptans are objectionable in fuel oils employed in homes orindustrial plants primarily because they are strongly and unpleasantlyoderiferous materials. Furthermore, they are very volatile and unstablecompounds and can present a safety problem if present in excessiveamounts. However, the prevailing commercial specification for mercaptansof 30 ppm (maximum), or 0.003 weight percent, is based upon odorconsiderations as this level represents the threshold at which thepresence of mercaptans is deflectable by odor. Because of the repugnantodor of mercaptans, a level about 30 ppm of mercaptan in the oil wouldrender the mere presence ofa fuel oil obnoxious in a home of industrialestablishment. In addition, since mercaptans are mild acids, they canalso contribute to a corrosion problem of the oil. Furthermore, amercaptan content above 30 ppm has been found to contribute to geltypesludgeformation in an oil, causing plugging in pipelines in which theoil is standing or flowing.

In accordance with the present invention, an extremely mildhydrogenation treatment has been developed for the reduction of totalacid number and/or mercaptan sulfur content in virgin oils which alreadymeet commercial total sulfur content requirements, i.e. a maximum sulfurcontent below 0.2 weight percent sulfur for home heating fuels. Thepresent invention accomplishes a reducton in total acid number and/ormercaptan sulfurcontent in oils which already meet commercial totalsulfur content requirements without blending such oils with high totalsulfur content oils prior to hydrodesulfurization of high totalsulfurcontent oils under severe conditions, as has been the practice inthe past. High total sulfur content oils not only require treatment in ahigh pressure and temperature hydrodesulfurization unit to accomplishhydrodesulfurization, but also require a highly active hydrogehave nowfound that total acid number and mercaptan content can be reduced undermuch milder hydrogenation conditions with a degenerated and deactivatedhydrogenation catalyst so that such feeds can be separately treated inanother reactor without unnecessarily consuming valuable space in highpressure reactors. There has not previously been a sufficiently mildhydrogenation process to make independent hydrogenation of these oilseconomic and therefore in hydrogenative treatment they formerly werereduced in total acid number or mercaptan sulfur content by aqueouscaustic treatment. However, this method may soon have to be abandonedbecause the aqueous effluent from caustic units represents anunacceptable stream pollutant under present-day environmental standards.

We have now discovered that the degree of hydrogenation required for thereduction of total acid number or mercaptan sulfur content in virginmiddle distillates to acceptable commercial levels where the nature ofthe crude oil source of these oils is such that these oils alreadysatisfy commercial total sulfur requirements, is so low that it iscommercially wasteful to blend these oils with hydrodesulfurizationfeeds wherein the nature of the crude oil source of the oil is such thata major portion of the total sulfur content of the feed must be alsoreduced. We have discovered that hydrogenative treatment for reductionof total sulfur requires treatment under hydrodesulfurization conditionswhich are unnecessarily severe for the low sulfur feeds of thisinvention. For example, we have found that straight run middledistillates which do not satisfy commercial total acid number and/ormercaptan content requirements but do satisfy commercial total sulfurrequirements without hydrotreatment can be separately treated to producecommercially acceptable levels in regard to total acid number and/ormercaptan content in units wherein chemical consumption requirements areonly from one to five, or even lower, standard cubic feet of hydrogenper barrel of feed (from 0.0l8 to 0.09 standard cubic meters per 100liters of feed) and unit hydrogen consumption including hydrogen lossesare less than 10 or standard cubic feet per barrel of feed (less than0.l8 to 0.27 standard cubic meters per 100 liters of feed The catalyticactivity required to accomplish such a slight chemical hydrogenconsumption is so correspondingly slight that use of an active or freshhydrodesulfurization or hydrogenation catalyst is not only wasteful butaccomplishes a level of hydrogenation which is not required by theprocess. To illustrate, a virgin middle distillate stream is ordinarilyrelatively olefin-free so that it contains only about one percent byvolume of olefins, and these olefins are relatively easy to hydrogenate.However, in accordance with the present invention. these olefins are nothydrogenated to a major extent because such olefin hydrogenation is notgenerally required to accomplish reduction in total acid number or toaccomplish reduction in mercaptan content to commercially acceptablelevels. However. ifthe hydrogenation conditions ofthe present inventionwere sufficiently severe, saturation of these olefins of itself wouldaccount for a chemical consumption of hydrogen of about nine standardcubic feet per barrel (0162 standard cubic meters per 100 liters), whichis higher than that generally required for the reduction for total acidnumber and mercaptan content in most feeds.

In order to diminish unnecessary chemical or unit hydrogen consumptionbeyond that which is required to reduce neutralization number and/ormercaptan sulfur content in a feed stream of this invention tocommercially acceptable levels, the present invention ordinarily employshydrogen pressures below psi (7 kg/cm and also employs as ahydrogenation catalyst a permanently deactivated catalyst as a fixedcompact bed in downflow operation, which catalyst has been prevouslyemployed in a separate but high pressure (600 psi or more, 4.2 kg/cm ormore) hydrogenation process. The catalyst is only transferred from thesevere hydrogenation process after it has experienced many regenerationcycles and its activity loss as compared to its original cycle is sosevere that it is no longer a viable catalyst in a high pressure, highhydrogen consumption process except by the use of excessive startof-runtemperatures, or unacceptably short cycle life before furtherregeneration is required. We have discovered, in accordance with thepresent invention, that these apparently hopelessly deactivated highpressure hydrogenation catalysts which would otherwise be discarded ordecomposed for recovery of valuable metals have a vestige ofhydrogenation activity remaining which is sufficient for the process ofthe present invention. It is emphasized, that the catalysts of thepresent invention would otherwise be discarded or destroyed as being ofinsufficient activity to be of further use in other refineryhydrogenation processes. These deactivated catalysts can be subjected toa final combustion regeneration for removal of carbon and a sulfidationwithin their original reactor and at the temperature of their originalreactor, prior to transfer to the mild temperature and pressure reactorof this invention. We have successfully employed in the process of thisinvention Group VI and Group VIII metal on alumina hydrogenationcatalysts, such as NiCoMo on alumina, which have experienced at leastfour or five regenerations by combustion of carbon until in about thefifth cycle the required start-of-run temperature to accomplish a givenproduct sulfur level in a fuel oil hydrodesulfurization process waselevated by 40 to 60F. (22.2 to 333C.) as compared to the initial cycle,thereby rendering the duration of its useful life in the fifth cycle,employing rising temperatures to compensate for desulfurization activityloss, unacceptably short. We have also employed in the process of thisinvention a deactivated nickel-tungsten-fluorine on silica-aluminahydrocracking catalyst which was sufficiently deactivated so that it wassufficiently inactive for further use as a compact fixed or stationarybed hydrocracking catalyst in downflow operation but still retainedsufficient hydrogenation activity to be of use under the mild conditionsof this invention wherein the temperatures and pressures were too low toeffect significant feed cracking but were sufficient for very mildhydrogenation. Residue hydrodesulfurization catalyst permanentlydeactivated in downflow operation as a compacted bed by feed metals canalso be employed in the present invention without prior demetallization.The only pretreatment required for these catalysts after deactivation intheir original processes and prior to similar downflow compact bed usein the process of the present invention is a possible combustiveregeneration and/or a possible sulfidation step. such as by passage of ahigh total sulfur-content oil over the catalyst underhydrodesulfurization conditions, after which these catalysts can beremoved from their original reactor to another or secondary reactor,preferably of smaller wall thickness and of different diameter. In theirsecondary reactor, these catalysts can be employed under low temperatureand pressure conditions for a long or indefinite duration, often withoutfurther sulfidat'ion or regeneration. We have found the small, residualhydrogenation activity remaining in these catalysts is ample for theiremployment to accomplish the limited hydrogenation required for thepresent invention. The following data show that the residualhydrogenation activity present in these aged catalysts is sufficient forreduction of total acid number via neutralization of naphthenic acids bya major extent, such as 75, 80 or 90 percent or more, and by reductionof mercaptan sulfur content via hydrogenation of mercaptan sulfurmolecules by a major extent such as by 60, 75, 80 or 90 percent or more,but is insufficient to concomitantly reduce total sulfur by more than aminor amount, i.e., by not more than 10, 20, 30, 40 and less than 50percent, and is also insufficient to reduce olefin content by more thana minor extent, i.e. not more than 20, 40 and less than 50 percent.

The process conditions for the present invention include temperaturesbetween 300 and 600F. (149 and 315C.), generally, and 400 to 550F. (204and 288C) preferably, hydrogen pressures below 100 or 150 psi (7 and10.5 kg/cm generally, and below 75 psi (5.15 kglcm preferably, liquidhourly space velocities between 3 and 10, generally, and between 4 and8, preferably and hydrogen circulation rates between 200 and 1,200 SCF/B(3.6 and 21.6 standard cubic meters per 100 liters), generally, and 300to 1,000 SCF/B (5.4 to 18 standard cubic meters per 100 liters),preferably. Hydrogen pressure requirements for this invention are verylow. Generally, only sufficient pressure to move the reactantsthroughthe system at the required space velocity will be adequate. Awide variety of Group V1 and Group Vlll catalytic metals are suitablefor the present invention. For example, nickelcobalt-molybdenum onalumina, cobalt-molybdenum, nickel-tungsten or nickel-molybdenum. Thesupport can be alumina, alumina-silica or silica-magnesia, as long asnon-cracking conditions are employed.

To illustrate the present invention, in one domestic refinery operationfor the preparation of both No. 2 home heating fuels and also kerosenesboiling broadly in the 350 to 700F. (176 to 371C.) range or, morenarrowly, in the 400 to 650F. (204 to 343C.) range, the refinery wassupplied by five different feed stocks boiling within these rangesoriginating from different crude sources. These five feed stocks aredescribed in Table l. Two of the feed stocks, a straight run West Texaskerosene and a West Texas straight run furnace oil did not meetcommercial requirements in regard to total sulfur content and thereforerequired high pressure hydrodesulfurization. A furnace oil from adistillation column to which an Ordovician crude was fed contained only0.11 weight percent total sulfur, meeting commercial specifications, butcontained 0.041 weight percent ofmercaptans and had a total acid numberless than 0.03, thereby failing to meet commercial specifications inregard to mercaptan content (30 ppm maximum) only, while meetingcommercial specifications in regard to total acid number (01 maximum). Afurnace oil from a distillation column to which a South Louisiana crudewas supplied contained only 0.10 weight percent total sulfur therebymeeting commercial specifications, contained a mercaptan sulfur contentof 0.0004,

also meeting commercial specifications, but had a total acid number of046-7, which is above the commercial specification of 0.1. A kerosenederived from a South Louisiana crude met commercial specifications inregard to total sulfur, mercaptan content, but not in regard to totalacid number, having a total acid number of 0.12 which exceeds themaximum allowable 0.10 commercial specification. The various feed stocksshown in Table 1 show that it is possible for a straight run middledistillate feed stock to meet commercial specifications in regard tototal sulfur content and in regard to total acid number, but not inregard to mercaptan sulfur content. It is also possible for a straightrun feed stock to meet commercial specifications in re gard to totalsulfur content and mercaptan sulfur content, but not in regard to totalacid number. It is also possible for a straight run middle distillate tomeet commercial specifications in regard to total sulfur content but notin regard to either total acid number or mercaptan sulfur content.

In accordance with the present invention, any straight run feed stockwhich fails "to meet commercial specifications in regard to total sulfurcontent must be treated in a high pressure vessel capable of accommo-'dating a pressure of 600 to 1,000 psig (42 to kg/cm or more and atemperature of 680F. (360C.) or more to accomplish hydrodesulfurizationin the presence of a highly active hydrodesulfurization catalyst, suchas a Group V1 and Group VIII metal on a non-cracking support, such asalumina, with or without less than about 1 percent of a non-crackingstabilizing amount of silica, usually in downflow-operation of feed oiland hydrogen. Common catalystic metals include nickel, cobalt,molybdenum, tungsten, etc. in various combinations. However, we have nowfound that straight run middle distillates which meet commercial totalsulfur requirements but fail to meet commercial requirements in regardto total acid number and/or mercaptan sulfur content can be charged to aseparate reactor, and at a relatively lower temperature which is alwaysbelow 650F. (343C), operated at a much lower pressure, such as psig (7kg/cm or less, with the same or a similar catalyst as was used in thehigh pressure hydrodesulfurization reactor as a downflow, compact bedbut in a permanently deactivated state in regard to the requirements ofthe high pressure reactor. In this manner, a smaller total flow ispassed through the high pressure reactor, said flow being diminished bythe feed charged directly to the low pressure reactor, permitting thediameter of the high pressure reactor to be greatly reduced. Since thethickness of the steel wall which is required in a high pressure andhigh temperature reactor increases greatly with reactor diameter (bycontrast, it is known that a thin-walled copper tube can withstandthousands of pounds of pressure if its diameter is only about A. of aninch or 0.63 cm), the present invention permits the high pressure andtemperature reactor to be constructed with a smaller diameter and alsowith a greatly diminished metal thickness, resulting in considerableeconomic savings. Since the feed streams by-passing the high pressurereactor are hydrotreated at only 100 psig (7 kg/cm or less, and at alower temperature, i.e. below 500 or 450F. (260 or 232C), than the highpressure reactor, the low pressure reactor will have a greatly reducedsteel thickness, as compared to the high pressure reactor, resulting ina considerable overall savings in the fabrication costs in the metalreactors.

The detailed characteristics of the five middle distillate feed stocksdescribed above are shown in Table l,

beds, or can comprise a portion of a single bed contained in the highpressure reactor, omitting the uppermost region of the bed, therebyutilizing in the low pressure reactor only the cleanest, mostmetals-free below. portion of the catalyst from the high pressurereactor.

TABLE 1 LOW SEVERlTY HYDROTREATING CHARGE INSPECTIONS South South WestWest Ordovician Louisiana Louisiana Texas Texas Furnace Oil Furnace OilKerosene Kerosene Furnace Oil Inspections Gravity, D287: APl 43.9 36.543.3 40.0 36.9 Distillation, D86: F.

Over Point 321(160C.) 361( 183C.) 331( 166C.) 340( 171C.) 338(170C.) EndPoint 617(325C.) 654(345C.) 496(258C.) 567(297C.) 708(375C.)

5% 372(189C.) 424(218C.) 359( 182C.) 385( 196C.) 446(230C.) 367(186C.)393(201C.) 413(212C.) 407(208C.) 480(249C.) 375( 191C.) 423(217C.)496(258C.) 383( 195C.) 443(228"C.) 508(264C.) 390(199C.) 5071 463(240C.)520(27 1C.) 399(2()4C.) 452(233C.) 499(259C.) 487(253C.) 532(278C.)408(209C.) 7071 513(267C.) 548(298C.) 419(215C.) 541(283C.) 566(297C.)432(222C.) 573(300C.) 596(313C.) 452(233C.) 520(271C.) 630(332C.)595(313C.) 622(328C.) 466(241C.) Sulfur, weight percent .11 .10 .69 .92Sulfur, ppm 267 Mercaptan Sulfur, D1323:

weight percent .041 .0004 .0006 .127 .11 Total acid number, D974 .03 .47.12 .06 Total acid number, D664 .46 Bromine number, D1159 6.7 7.4

No additional catalyst cost is required for operation of the lowpressure reactor, which is the reactor of the present invention, sinceit operates with catalyst that has been deactivated by repeatedregencrations in the high pressure reactor until it is no longer ofcommercial utility in the high pressure reactor. The deactivated highpressure catalyst is sult'idcd if required in the high pressure reactorprior to withdrawal therefrom at a temperature of about 600 to 650F.(315 to 343C.) by passage of high sulfur-content oil therethrough. Ifrequired, it can also be regenerated by combustion in the high pressurereactor. Then the catalyst can be removed from the high pressure reactorby any suitable means, such as through a plug in the bottom thereof.

The catalyst for reuse in the low pressure reactor can comprise thecatalyst from the high pressure reactor in its entirety, or, since feedoil is passed downwardly through the high pressure reactor, the reusedcatalyst can comprise only the bottom bed of a multiplicity of It ispossible to utilize the entire bed from the high pressure reactor in thelow pressure reactor if the total amount of catalyst is required in thelow pressure reac- 35 tor and if the average contamination of the totalcatalyst bed in the high pressure reactor is not excessive. The catalystremoved from the high pressure reactor is then replaced by a similaramount and quality of fresh catalyst.

40 Table 2, below, shows the test conditions employed and the resultsobtained when the first three feed stocks listed in Table 1 (whichalready met commercial total sulfur requrements and therefore did notrequire high pressure hydrodesulfurization) were treated under the 45low pressure hydrogen test conditions of this invention 50 pact catalystbed.

TABLE 2 LOW SEVERITY HYDROTREATING WITH AGED CATALYSTS SUMMARIZED CHARGESTOCK AND TYPICAL PRODUCT INSPECTIONS Ordovician South Louisiana SouthLouisiana Feed from Table l Furnace Oil Furnace Oll Kerolene OperatingConditions:

Catalyst Aged Aged Aged Reactor Temperature: F. 500(260C.) 475(246C.)450(232'C.) Reactor Pressure: pailgI (7 k lcm') 100(7 k lcm) 100(7 klcrn) Space Velocity: Vol/ r/Vol 4.8 4.8 4,8 Gas Circulation Rate:

SCF/B FF 1000 1000 1000 (I9 mllOO liters) (l8 In /100 liters) (Illm"/l00 liters) Gas Hydrogen Content:

Volume percent 85 85 85 Liquid Product Yield:

Volume ercent FF 100 I00 I00 Hydrogen ulfide Yield:

TABLE 2 Continued LOW SEVERITY HYDROTREATING WITH AGED CATALYSTSSUMMARIZED CHARGE STOCK AND TYPICAL PRODUCT INSPECTIONS Ordovician SouthLouisiana South Louisiana Feed from Table I Furnace Oil Furnace OilKerosene Weight percent FF 0.06 0.04 0.0]

Fresh Hydrotreated Fresh Hydrotreated Fresh Hydrotreated Feed ProductFeed Product Feed Prodw Inspections Gravity, D287: API 43.9 43.8 36.536.3 43.3 43.2 Distillation, D86: F.

Over Point 32l(l6lC.) 338(l70C.) 36l(l82C.) 357(18lC.) 33l(l66C.)340(I7IC.) End Point 617(325C.) 629(332C.) 654(345C.) 629(332C.)496(258C.) 503(262C.) 10% 385(196C.) 388(198C.) 446(230C.) 446(230C.)367( 186C.) 369(187C.) 423(2I7C.) 43l(222C.) 496(258C.) 495(257C.) 383(I95C.) 385(196C.) 50% 463(239C.) 474(245C.) 520(27IC.) 5l9(27lC.)399(204C.) I(205C.) 70% 513(267C.) 523(273C.) 548(287C.) 545(285C.)4I9(2l5C.) 420(215C.) 90% 573(301C.) 583(306C.) 596(3l3C.) 595(313C.)452(2313C.) l(233C.) Mercaptan Sulfur,

D1323: weight percent 0.041 0.0009 0.0004 0.0006 Total Acid Number, D9740.03 0.47 0.03 0.12 0.03 Sulfur, ppm 267 186 Sulfur, weight percent 0.1l 0.05 0.10 0.06

Color, Saybolt, D l 56 Table 2 shows that the present process improvesnot only mercaptan sulfur content and total acid number but alsoimproves color properties of the feed oil. It also shows there issubstantially 100 percent yield of furnace oil or kerosene in thepresent process.

Table 3, presented below, presents additional test data and productspecifications when treating the Ordovian furnace oil under still othersingle pass conditions than those shown in Table 2.

TABLE 3 OPERATING CONDITIONS Catalyst NiCoMo-on-alumina 4 Aged Volume:cc 262.0 Weight: gms 238.9 Age Days 34.5 BBL/LB FF 12.5 (.004353 mVg)Period Length: hours 63.0 Operating Conditions Reactor Tempera\ure:'F.430.0 I r (221C) Reactor Pressure: psig l0l.()

(7.07 kglcni Space Velocity FF Vol/Hr/Vul 3.98

Wt/Hr/Wt 3.53 Reactor Gas FF SCF/BBL 604.0

(10.9 SCM/IOOL) Hydrogen Content:

percent by volume 85.6 Weight Balance O/l: percent 99.6 HydrogenConsumption: SCF/BBL FFC [4.0

Therefore, in the present proc'ess,there is essentially no removal ofsulfur atoms from the interior of mole cules as occurs in high pressurehydrodesulfurization with high sulfur'content feeds and which splits thefeed molecules into lower molecular weight fragments boiling in thenaphtha range, or lower.

The catalyst employed in all the tests-was NiCoMoon-alumina which waspreviously deactivated in high pressure (600 psig or 42 kg/cmhydrodesulfurization 7 runs employing straight-run middle distillate oilfeed stocks which failed to meet the 0.2 weight percent total sulfurspecifications. An example of the extent'of deactivation of such acatalyst in a high pressure process is illustrated in FIG. 7. The testsillustrated in FIG. 7 were performed at a temperature of 620 -700 F.(326-37 1C.), 600 psig (42 kg/cm 5.85 LHSV with 900 SCF/B (16.2 SCMIOOL)of 85 percent hydrogen reactor gas. The charge oil was a West Texasfurnace oil containing 0.98 weight percent sulfur. The first cycle ofthe high pressure (600 psig or 42 kg/cm hydrodesulfurization catalystexhibited the upper temperature response curve shown in FIG. 7, whilethe lower curve of FIG. 7 shows the temperature response characteristicsin thefifth cycle of the catalyst with the same feed, withcombustionregeneration between cycles, after whcih 268 barrels of oilper pound of total catalyst (0.094 m /g) was passed throughthe reactor.FIG. 7 shows the aged catalyst was -60F. (27.8

" to 700F. (327 to'37l.C.) reactor temperature range in which thecatalyst was aged. Each regeneration of the catalyst results in a higherrequired start-of-run temperature and a shorter time of operation in thesubsequent cycle.

The aged catalyst was then presulfided in the high temperature andpressure hydrodesulfurization reactor with Ordovician furnace oil for 12hours at: 650F. (343C). 4.0 LHSV at 1000 psig kg/cm). Thereupon. it wasemployed as a catalyst in'the low temperature and pressure reactor ofthis inventionwith the results shown in the following figures.

FIG. 1 shows the relationship in the processof the present inventionbetween non-mercaptan or total sul fur content reduction and mercaptandesulfurization number reduction in tests conducted at 100 psig (=7-kglcm 400 to 650F. (204 to 343C), 4-8 LHSV,

300 -l,000 SCF H2)/B (5.4-18 SCM/IOOL). The solid circles of FIG. 1represent theOrdovicianufurnace oil feed of Table I while the crossesindicatethe West Texas kerosene feed of Table I. As shown in FIG. I, theprocess of this invention removed about weight:

percent of the mercaptan sulfur before removing only about 15 percent ofthe total sulfur content of the feed, showing the high selectivity ofthe present process for removal of mercaptan sulfur while not removingtotal sulfur. FIG. 1 shows a 50 percent reduction in mercaptan sulfurcontent occurred with only about 1 or 2 percent reduction in totalsulfur content.

FIG. 2 shows the relationship between nonmercaptan or totaldesulfurization and percent reduction in total acid number with testsconducted under the conditions of the present invention which include100 psig (7 kglcm 400 to 650F. (204 to 343C), 4-8 LHSV and 300 -I,00OSCF (85% H )/B (5.4 -I8 SCM/IOOL). In FIG. 2, the crosses indicate theSouth Louisiana kerosene feed of Table 1 and the solid circles indicatethe South Louisiana furnace oil feed of Table 1. FIG. 2 shows that theprocess of the present invention is capable of reducing the total acidnumber of a feed oil by at least 80 percent while reducing the totalsulfur content of the oil only 20 percent, again showing the highselectivity of the present process for treatment of low totalsulfur-containing oils. FIG. 2 shows a 50 percent reduction in totalacid number occurred with less than about a five percent reduction intotal sulfur content.

FIGS. 1 and 2 both show that the reduction in mercaptan sulfur contentand the reduction in total acid number both occur much more readily thanthe undesired total desulfurization reaction. FIGS. 1 and 2 show that90-95 percent mercaptan desulfurization and 80 percent total acid numberreduction occur with only 20 percent total desulfurization.

FIG. 3 illustrates the results of a similar test with the same agedcatalyst at 100 -I50 psig (7 10.5 kg/cm The solid circles represent aheavy FCC naphtha feed (not illustrated in Table 1), the hollow circlesrepresent the WestTexas kerosene feed of Table 1, and the trianglesrepresent the West Texas furnace oil feed of Table 1. FIG. 3 shows that,the saturation of olefins occurs at even a slower rate thannon-mercaptan or total desulfurization, i.e. at 20 percent totaldesulfurization only about 6 percent olefin saturation occurred.Therefore, the conditions of the present invention are too mild toaccomplish significant olefin saturation. This is an important featureof the present invention because, assuming atypical middle distillatefeed contained 1 percent olefin by volume, the saturation of theseolefins alone would account for a chemical hydrogen consumption of about9 SCF/B (0.162 SCM/IOOL).

FIGS. 4, 5 and 6 show results obtained with a fresh hydrogenationcatalyst having a similar composition as that employed in the tests ofthe other Figures, except that the catalyst represented by the lowestcurve of FIG. 4 was previously aged for two cycles in a prior highpressure hydrogenation process. These figures show that the presentinvention can be practiced with a fresh as well as an aged catalyst.although the fresh catalyst will require milder conditions to maintainthe low hydrogen consumption levels of this invention. In FIGS. 4, 5Aand 5B the feed stock is the Ordovician furnace oil of Table l. Thetests of FIG. 4 were performed with a circulation of 1,000 SCF/B (l8SCM/IOOL) of 85 percent hydrogen at the temperatures, pressures andspace velocity conditions indicated. FIG. 4 shows that in accordancewith the present invention the feed mercaptan sulfur content can bereduced from a value of 410 in the original feed stock to values as lowas 8, 10 or ppm at 450F. (232C).

and can be reduced to a value approaching 0 ppm at a temperature of500F. (260C.). FIG. 4 shows very little advantage in increasing thepressure from 100 to 200 psi (7 to 14 kg/cm for removal of mercaptansulfur. FIG. 4 also shows that more than percent mercaptan removaloccurred in the process for the feed oil to meet the commercialspecification of 30 ppm mercaptan content.

FIGS. 5A and 58, represent tests made with the Ordovician furnace oilfeed of Table I and show that hydrogen circulation rate does not have agreat effect upon the achievement of 30 ppm of mercaptan sulfur in theoil at the conditions tested.

The tests of FIG. 6 were made with the South Louisiana furnace oil ofTable I at psig (7 kglcm with 1,000 SCF/B (18 SCM/100L) of 85 percenthydrogen. These tests show that feed total acid number can be reduced ina feed which had a value of 0.47, to a value of 0.1 at temperaturesbelow 450 to 500F. (232 to 260C.) depending upon space velocity. FIG. 6shows that nearly 80 percent reduction in acid content occurred in theprocess for the feed oil to meet the commercial specification of 0.1total acid number.

FIGS. 4, 5A, 5B and 6 illustrate that a wide range of low severitytemperature, pressure and space velocity conditions can be employed witha hydrodesulfurization catalyst to accomplish the required commerciallow mercaptan sulfur content and low total acid number values inaccordance with this invention.

As stated above, commercial specifications for No. 2 furnace oil requirea maximum total sulfur content of 0.2 weight percent sulfur for homeheating fuel, a maximum mercaptan content of 30 ppm (0.003 weightpercent) and a total acid number of less than 0.1. Total acid number isdefined as milligrams of potassium hydroxide (KOH) that is required toneutralize all acidic constituents present in I gram of oil sample (mgKOH/gm sample), according to ASTM test D664 or D974, 1968 Book of ASTMStandards, Volume 17, page 235. About the same results are obtained intotal acid number when ASTM test method D974, which employs colorimetrictitration, is employed, as in the case of method D664, which employspotentiometric titration. Mercaptan sulfur content is defined as gramsof mercaptan sulfur per 10 grams of oil.

It is seen that of the middle distillates listed in Table 1, only theWest Texas middle distillates contained more than commercialspecifications in regard to total sulfur content. Therefore, it isnecessary to hydrodesulfurize these oils at a pressure above 600 psig(42 kg/cm and preferably in the 1,000 to 2,000 psig (70 to kglcm rangedisclosed above to reduce their sulfur content to 0.2 weight percentsulfur. However, the Ordovician middle distillate and the SouthLouisiana middle distillates both meet commercial total sulfur contentrequirements and therefore do not require severe hydrodesulfurization toaccomplish reduction of total sulfur content. However, under thepractice of the prior art, the Ordovician and South Louisiana middledistillates would have been blended with the West Texas middledistillates to obtain a total refinery middle distillate blend forfeeding to the high pressure hydrodesulfurization unit because under thesevere hydrogenation conditions required for the reduction of totalsulfur content of the West Texas middle distillates, the 410 ppmmercaptan content of the Ordovician middle distillate would easily bereduced to the pressure reactor. This practice is based upon outdiscovery that for straight run middle distillates the severity of theoperation required for the reduction of total acid number and thereduction of mercaptan sulfur content by hydrotreatment is much milderthan is required for the reduction of total sulfur content.

The following calculations are presented to illustrate that relativelyminuscule quantities of chemical hydrogen consumption are required toaccomplish the required reductions in total acid number and mercaptansulfur content in accordance with this invention.

To reduce the total acid number via hydrogenation, the most prevalantreaction involved is the reaction of an organic naphthenic acid withhydrogen to produce a saturated hydrocarbon plus water, according to thefollowing equation:

From this equation it is seen that three moles of hydrogen are requiredto saturate one mole of organic acid. The hydrogenation method ofneutralization is the method employed in accordance with the presentinvention.

The ASTM neutralization test method reacts the organic acid with KOH toproduce a salt plus water according to the equation:

KOH (It-(1 1110 on o it is seen from this equation that one mole of KOHis required to neutralize one mole of organic acid.

lfthe neutralization or total acid number ofa leedoil is known. theamount of hydrogenrequired to be consumed when reducing the total acidnumber to the value required by commercial specifications can be calculated as follows:

Total acid number mg/KOH/gram sample pull density ofsample, gm/ccMolecular weight of KOH 56,!08 mg/mole A total acid number reduction intotal acid number (total acid number of untreated oil minus the acidnumber of the treated product) H consumption (SOF/B) 3785cc l'gal.

1 mole acid 1 mole KOH 3 gm moles H mole acid saturated 42.0 gal. 379set Bbl mole (A total acid no.)(e,,; )(7.10) SCF H /Bbl oil 1 mole 453.6gm molcs To convert SCF H- /Bbl oil to SCM/lOOL multiply by 0.018. t Inan actual example based on the South Louisiana middle distillate ofTable l which has a total acid number of 0.46 wherein the specificgravity of the oil was 36.5 APl (0.8423 g/cc), to reduce the total acidnumber (Atotal acid number) from 0.46 to 0.10 (A 0.36) the hydrogenconsumption is therefore the (A total acid number) times the density ofthe oil times 7.10; or

Hydrogen consumption =0.36 X 0.8423 X 7.10 2.2 standard cubic feet ofhydrogen per barrel (0.04 SCM/lOOL).

It is seen from the above sample calculation that the hydrogenrequirement to reduce the total acid number of the South Louisianamiddle distillate to meet commercial standards is extremely small, aslong as the middle distillate already meets commercial standards inregard to total sulfur content. Therefore, in accordance with thisinvention not more than about 5 or 10 standard cubic feet of hydrogenper barrel (0.09 to 0.18 SCM/l00L) of middle distillate are required interms of chemical hydrogen consumption to reduce total acid number of anoil sufficiently to meet commercial requirements of the oil. In terms oftotal unit hydrogen requirement, including solubility losses, therequirement in hydrogen need not exceed 15, 20, 25 or 30 standard cubicfeet per barrel (0.27, 0.36, 0.45 or 0.54 SCM/IOOL).

It can be shown that hydrogen requirements for reducing mercaptan sulfurcontent to commercially acceptable levels by hydrogen treatment inaccordance with the present invention can be even smaller than thatshown above for the reduction of total acid number. The reactioninvolved for the reduction of mercaptan sulfur via hydrogenationproceeds as follows:

From the above equation, it is seen that two moles of hydrogen arerequired for each mole of mercaptan sulfur which is removed.

The analysis of mercaptans is usually presented in units of parts permillion, as follows:

mole KOH mg KOH Hydrogen consumption in SCF/B for mercaptan removal =AMercaptan S content 106 g Oil 3785 cc 42.0 gal 1 l and generally willnot exceed or standard cubic feet per barrel (0.090 or 0.18 SCM/lOOL) interms of chemical hydrogen consumption, or will not exceed 15,

M t S grns ercap an (gcmc s) gal mercautau mercnptan 2 g moles H gms 1mole (gm mole mercaptan) X MW...

379 SCF 1 mole gas (A Mercaptan S content) e (3785)(42)(2)(379) Toconvert SCF HyjBbl to SCM/IOOL multiply by 0.018.

The Ordorician middle distillate shown in Table 1 contained 410 ppm ofmercaptan. lts API was 43.9 (0.8067 gm/cc). lts mean average boilingpoint was 451F. (233C). lts molecular weight, from AP1 and mean averageboiling point, is 192. Therefore, to reduce the mercaptan sulfur in thecharge from 0.041 weight percent, or 410 ppm, to a product containing 30ppm, the hydrogen consumption [(410 30) (0.8067) (0.266)]/l92 0.4standard cubic feet per barrel (0.0072 SCM/lOOL).

It is seen from the above sample calculation that the hydrogenrequirement to reduce the mercaptan content of the Ordovician middledistillate to meet commercial standards is extremelysmall, as long asthe middle distillate already meets commercial standards in regard tototal sulfur content. Therefore, in accordance with this invention notmore than about 5 or 10 standard cubic feet of hydrogen per barrel ofmiddle distillate (0.09 or 0.18 SCM/lOOL) are required in terms ofchemical hydrogen consumption to reduce mercaptan content of an oilsufficiently to meet commercial requirements of the oil. In terms oftotal unit hydrogen requirement. including solubility losses and lossesin the hydrogen off-gas, the requirement in hydrogen need not exceed 15,or standard cubic feet per barrel (0.27, 0.36 or 0.45 SCM/lOOL).According to the Oil and Gas Journal, Feb. 17, 1969, Volume 67, No. 7.page 78, hydrogen solubility losses are about 0.4 SCF/B (0.0072SCM/IOOL) times the pressure in atmospheres. Therefore. at 100 psi (7kg/cm unit pressure, hydrogen solubility losses are 0.4 times 100/l5 z 3SCF/B (0.054 SCM/lOOL). Table 3 shows total unit hydrogen requirementsof only 14 standard cubic feet per barrel (0.0252 SCM/lOOL) whentreating the Ordovician middle distillate of Table l.

The above two calculations show the actual mercaptan sulfur removal oracid number reduction is accomplished with hydrogen chemicalconsumptions only slightly above zero to less than 3 standard cubic feetper barrel (0.054 SCM/lOOL).

It is again seen that for a middle distillate which meets commercialrequirements in regard to total sulfur content, the hydrogen consumptionrequirement for the reduction of mercaptan sulfur to commerciallyacceptable levels is extremely small and can be below gm mole mercaptan453.6 gm mole 20 or 25 standard cubic feet per barrel (0.027, 0.36 or0.450 SCM/IOOL) in terms of total unit hydrogen consumption, includinglosses. In fact, when a feed meets commercial total sulfur requirementsbut does not meet commercial total acid number requirements orcommercial mercaptan content requirements, the total chemicalconsumption to meet both of these requirements should not exceed 5 or 10standard cubic feet per barrel (0.09 or 0.18 SCM/lOOL), or 15 to 25standard cubic feet per barrel (0.27 to 0.45 SCM/lOOL) when solutionlosses are considered.

We claim:

1. A relatively low pressure hydrotreating process performed in a firstand relatively low pressure reactor comprising passing a first feed oilcomprising middle distillate straight run feed oil and hydrogendownwardly over a hydrodesulfurization catalyst that has beendeactivated in a prior relatively high pressure hydrodesulfurizationprocess, said prior process being operated in a second and high pressurereactor in downflow operation with a second feed oil at a pressure of atleast 600 psi and at a temperature between 650 and 800F. until saidcatalyst permanently possessed insufficient desulfurization activity forsaid high pressure process, said catalyst thereupon being removed fromsaid second reactor and charged to said first and low pressure reactorfor hydrotreatment of said first feed oil at a pressure no higher thanabout 150 psi and at a temperature between 400 and 550F.

2. The process of claim 1 wherein not more than 30 weight percent of thetotal sulfur in the feed oil is removed in the low pressure reactor.

3. The process of claim 1 wherein said middle distillate feeds boil inthe range 350 to 700F.

4. The process of claim 1 wherein the catalyst comprises supported GroupVI and Group VIII metals and the pressure is no higher than psi.

5. The process of claim 1 wherein the temperature in said low pressurereactor is between 400 and 550F.

6. The process of claim 1 wherein the temperature in said low pressurereactor is below 500F.

7. The process of claim 1 wherein the temperature in said low pressurereactor is below 450F.

8. The process of claim 1 wherein the LHSV in said low pressure reactoris between 4 and 8.

9. The process of claim 1 wherein not more than 20 weight percent ofthetotal sulfur in the feed is removed in the low pressure reactor.

10. The process of claim I wherein said middle distillates are furnaceoil, kerosene or jet fuel.

11. The process of claim 1 wherein chemical hydrogen consumptionexcluding unit losses in said low pressure reactor is less than standardcubic feet per barrel.

12. The process of claim 1 wherein unit hydrogen consumption includinglosses in said low pressure reactor is less than standard cubic feet perbarrel.

13. The process of claim 1 wherein the pressure in the low pressurereactor is below 75 psi.

14. The process of claim 1 wherein the chemical hydrogen consumption inthe low pressure reactor is less than 5 standard cubic feet per barrelof feed oil.

15. A combination first relatively high pressure and second relativelylow pressure hydrotreating process comprising passing a first middledistillate straight run oil having a total sulfur content greater than0.2 weight percent derived from a first crude oil downwardly over asupported Group VI and Group VIII hydrodesulfurization catalyst in afirst and high pressure hydrodesulfurization rector at a pressure above600 psi and at a temperature between 650 and 800F. to reduce the totalsulfur content of said first oil below 02 weight percent until saidcatalyst is permanently deactivated and possesses insufficientdesulfurization activity for said high pressure process, removing saidcatalyst from said high pressure reactor and passing it to a second andrelatively low pressure reactor operated at a pressure below about 150psi, passing a second middle distillate oil having a total sulfurcontent less than 0.2 weight percent derived from a second crude oildownwardly over said deactivated catalyst at a pressure no higher thanabout 150 psi and at a temperature between 400 and 550F. so that thechemical hydrogen consumption in said second reactor is above 0 butbelow 10 standard cubic feet per barrel.

16. The process of claim 15 wherein not more than 30 weight percent ofthe total sulfur in the feed oil is removed in the low pressure reactor.

17. The process of claim 15 wherein said middle distillate feeds boil inthe range 350 to 700F.

18. The process of claim 15 wherein the catalyst comprises supportedGroup VI and Group VIII metals and the pressure is no more than psi.

19. The process of claim 15 wherein the temperature in said low pressurereactor is between 400 and 550F.

20. The process of claim 15 wherein the temperature in said low pressurereactor is below 500F.

21. The process of claim 15 wherein the temperature in said low pressurereactor is below 450F.

22. The process of claim 15 wherein the LI-lSV in said low pressurereactor is between 4 and 8.

23. The process of claim 15 wherein not more than 20 weight percent ofthe total sulfur in the feed is removed in the low pressure reactor.

24. The process of claim 15 wherein said middle distillates are furnaceoil, kerosene or jet fuel.

25. The process ofclaim 15 wherein chemical hydrogen consumptionexcluding unit losses in said low pressure reactor is less than 5standard cubic feet per barrel.

26. The process of claim 15 wherein there is a color improvement in themiddle distillate feed to the low pressure reactor 27. The process ofclaim 15 wherein there is substantially a 100 percent yield in themiddle distillate feed to @32 3 UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION .Patent No, 318501744 I Dated November 26, 1974 Inventor)R. A. Plundo, T. C. Readal and J. R. Strom It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Col. 2, line 1, after "fuel" insert -but Col. 2, line 17, "hign" shouldread high-- Col. 2, 'line 23, "oil" should read -0.l,--

Col.- 2, line 36, "deflectable" should read --detectable- Cols. 7 and 8,Table 1, under "South Louisiana Furnace Oil" opposite "70%", "548 (298C.should read Cols. 7 and 8, Table 2, under "Ordovician Furnace Oil"opposite "Gas Circulation Rate: SCF/B FF", "l9 m /lO0 liters" shouldread --l8 m /l0 O liters-- Col. 13, line 12, "out" should read --our-Col. 15, last line of equation (0266) should read (0.266)-- 3.31190 anslead this 22m; day of .---.pr1l l 75.

Attest:

C criminal BAKE? PUT C. Lil-1552' Commissioner of Patents j'lttestingOfficer and Trademarks

1. A RELATIVELY LOW PRESSURE HYDROTREATING PROCESS PERFORMED IN A FIRSTAND RELATIVELY LOW PRESSURE RECTOR, COMPRISING PASSING A FIRST FEED OILCOMPRISING MIDDLE DISTILLATE STRAIGHT RUN FEED OIL AND HYDROGENDOWNWARDLY OVER A HYDRODESULFURIZATION CATALYST THAT HAS BEENDEACTIVATED IN A PRIOR RELATIVELY HIGH PRESSURE HYDRODESULFURIZATIONPROCESS, SAID PRIOR PROCESS BEING OPERATED IN A SECOND AND HIGH PRESSUREOF AT LEAST FLOW OPERATION WITH A SECOND FEED OIL AT A PRESSURE OF ATLEAS 600 PSI AND AT A TEMPERATURE BETWEEN 650* AND 800*F. UNTIL SAIDCATALYST PERMANENTLY POSSESSED INSUFFICIENT DESULFURIZATION ACTIVITY FORSAID HIGH PRESSURE PROCESS, SAID CATALYST THEREUPON BEING REMOVED FROMSAID SECOND REACTOR AND CHARGED TO SAID FIRST AND LOW PRESSURE REACTORFOR HYDROTREATMENT OF SAID FIRST FEED OIL AT A PRESSURE NO HIGHER THANABOUT 150 PSI AND AT A TEMPERATURE BETWEEN 400* AND 550*F.
 2. Theprocess of claim 1 wherein not more than 30 weight percent of the totalsulfur in the feed oil is removed in the low pressure reactor.
 3. Theprocess of claim 1 wherein said middle distillate feeds boil in therange 350* to 700*F.
 4. The process of claim 1 wherein the catalystcomprises supported Group VI and Group VIII metals and the pressure isno higher than 100 psi.
 5. The process of claim 1 wherein thetemperature in said low pressure reactor is between 400* and 550*F. 6.The process of claim 1 wherein the temperature in said low pressurereactor is below 500*F.
 7. The process of claim 1 wherein thetemperature in said low pressure reactor is below 450*F.
 8. The processof claim 1 wherein the LHSV in said low pressure reactor is between 4and
 8. 9. The process of claim 1 wherein not more than 20 weight percentof the total sulfur in the feed is removed in the low pressure reactor.10. The process of claim 1 wherein said middle distillates are furnaceoil, kerosene or jet fuel.
 11. The process of claim 1 wherein chemicalhydrogen consumption excluding unit losses in said low pressure reactoris less than 10 standard cubic feet per barrel.
 12. The process of claim1 wherein unit hydrogen consumption including losses in said lowpressure reactor is less than 15 standard cubic feet per barrel.
 13. Theprocess of claim 1 wherein the pressure in the low pressure reactor isbelow 75 psi.
 14. The process of claim 1 wherein the chemical hydrogenconsumption in the low pressure reactor is less than 5 standard cubicfeet per barrel of feed oil.
 15. A combination first relatively highpressure and second relatively low pressure hydrotreating processcomprising passing a first middle distillate straight run oil having atotal sulfur content greater than 0.2 weight percent derived from afirst crude oil downwardly over a supported Group VI and Group VIIIhydrodesulfurization catalyst in a first and high pressurehydrodesulfurization reactor at a pressure above 600 psi and at atemperature between 650* and 800*F. to reduce the total sulfur contentof said first oil below 0.2 weight percent until said catalyst ispermanently deactivated and possesses insufficient desulfurizationactivity for said high pressure process, removing said catalyst fromsaid high pressure reactor and passing it to a second and relatively lowpressure reactor operated at a pressure below about 150 psi, passing asecond middle distillate oil having a total sulfur content less than 0.2weight percent derived from a second crude oil downwardly over saiddeactivated catalyst at a pressure no higher than about 150 psi and at atemperature between 400* and 550*F. so that the chemical hydrogenconsumption in said second reactor is above 0 but below 10 standardcubic feet per barrel.
 16. The process of claim 15 wherein not more than30 weight percent of the total sulfur in the feed oil is removed in thelow pressure reactor.
 17. The process of claim 15 wherein said middledistillate feeds boil in the range 350* to 700*F.
 18. The process ofclaim 15 wherein the catalyst comprises supported Group VI and GroupVIII metals and the pressure is no more than 100 psi.
 19. The process ofclaim 15 wherein the temperature in said low pressure reactor is between400* and 550*F.
 20. The process of claim 15 wherein the temperature insaid low pressure reactor is below 500*F.
 21. The process of claim 15wherein the temperature in said low pressure reactor is below 450*F. 22.The process of claim 15 wherein the LHSV in said low pressure reactor isbetween 4 and
 8. 23. The process of claim 15 wherein not more than 20weight percent of the total sulfur in the feed is removed in the lowpressure reactor.
 24. The process of claim 15 wherein said middledistillates are furnace oil, kerosene or jet fuel.
 25. The process ofclaim 15 wherein chemical hydrogen consumption excluding unit losses insaid low pressure reactor is less than 5 standard cubic feet per barrel.26. The process of claim 15 wherein there is a color improvement in themiddle distillate feed to the low pressure reactor.
 27. The process ofclaim 15 wherein there is substantially a 100 percent yield in themiddle distillate feed to the low pressure reactor.